A compressor, in particular high pressure, comprises one or several rotating discs (rotor), vaned or not and one or several fixed impellers (rectifier stages).
A turbine, in particular high pressure, comprises several rotating discs (rotor), vaned or not, and one or several fixed impellers (nozzle stages).
The rotating discs generally include peripheral grooves wherein vanes are nested, or are carried out in a single piece with the vanes, which are then machined on the periphery of the discs (the discs of this type are called integrally vaned discs).
The different discs can be assembled coaxially by bolting, by electron beam welding or, by rotational, inertial or pilot friction welding.
The welding via rotational friction consists in strongly pushing a disc fixed in rotation against another disc that is rotating around its axis and which is fixed in translation, by applying on these discs a force according to an axis corresponding to their main revolution axis. The friction of the surfaces of the discs in contact releases a large quantity of heat which raises the temperature of these surfaces in contact and allows them to be assembled by welding thanks to the plastic deformation of the materials of the discs.
This type of welding has the advantage of hardly altering the mechanical properties of the materials and of being able to be executed rapidly. However, it generates high-frequency and high-intensity vibrations, which can favour the formation of cracks due to fatigue with a large number of cycles, in particular on thin zones as well as in the hubs of these discs.
It has been proposed to dampen the vibrations in an axial plane of the hubs of the discs using steel expansion rings with a generally conical section, and which comprise staggered slots connected by bridges of material. The rings are placed inside the hubs of the discs during welding; an axial force is applied on the rings, which tends to displace them radially via their internal conical portion, so that they come into contact with the internal surface of the hubs and so that they dampen the vibrations in the axial plane of these hubs. However, when the diameter of the hubs is substantial, the axial force applied on the rings is substantial. The rings are furthermore difficult to remove at the end of welding, and risk scratching the internal surface of the hubs.
Finally, the hubs of the discs generally present different inner diameters and uncontrolled coaxial misalignments, therefore random, which are intrinsic to the process of welding via friction and which can reach 0.3 mm, which renders the use of these rings very delicate.
It has also been proposed, in FR 2848132, a damper suited for reducing the vibrations of components during the welding by friction, comprising a generally annular body having a spiral-shaped slot formed within.
Moreover, in the field of pipelines, a set of mandrels has been proposed, each comprising internal and external jaws suited to engage with sections of pipe intended to form the pipeline. However, in order to guarantee a good maintaining of the sections of pipes during the welding by friction, the jaws deform them locally thanks to corresponding bosses. Such information cannot be applied to hubs of turbomachines, in particular of a compressor or of a turbine, in that the latter must under no circumstances be damaged during welding.